<div class="g-contaner">
  <div class="g-btn">Hover Me</div>
  <p class="content">
    能够适配任意高度。能够适配任意高度。能够适配任意高度。
  </p>
</div>

<div class="g-contaner">
  <div class="g-btn">Hover Me</div>
  <p class="content">
    能够适配任意高度。能够适配任意高度。能够适配任意高度。能够适配任意高度。能够适配任意高度。能够适配任意高度。
  </p>
</div>

<style>
  body,
  html {
    width: 100%;
    height: 100%;
    display: flex;
    flex-direction: row;
    padding: 20px;
  }

  .g-contaner {
    width: 300px;
  }

  p {
    width: 200px;
    max-height: 0;
    box-sizing: border-box;
    line-height: 24px;
    background: #ddd;
    overflow: hidden;
    transition: all .3s linear;
  }

  .g-btn {
    width: 80px;
    padding: 5px;
    border: 1px solid #333;
    margin-bottom: 10px;
    cursor: pointer;
  }

  .g-btn:hover~.content {
    max-height: 300px;
  }
</style>